My invention comprises improvements in a hydrokinetic torque converter and lock-up clutch assembly of the kind shown, for example, in U.S. Pat. No. 4,509,389, which is assigned to the assignee of this invention. That patent describes a three-element torque converter including a turbine and an impeller located in a common converter housing wherein a clutch cavity is formed in the converter housing between the radial wall of the housing and the turbine, the radial wall of the housing being proximate to an engine crankshaft which is drivably connected to the impeller through the converter housing.
The construction of the '389 patent includes a friction disc in the form of a piston plate having a friction surface on its outer margin. The friction surface on the piston plate is adapted to engage a friction surface formed on an adjacent annular wall of the converter housing. The inner margin of the plate is supported by a turbine hub to which the turbine is connected. The piston plate, together with the adjacent wall of the converter housing, define a control pressure space which is pressurized with control fluid, thereby establishing radial fluid circulation across friction surfaces.
A damper assembly is used to connect drivably an outward radial portion of the piston plate to the turbine hub. Thus, when the clutch is applied, torque is distributed mechanically through the clutch from the engine crankshaft to the turbine, thus bypassing the hydrokinetic torque flow path through the torque converter. When the clutch is disengaged, all the torque is distributed from the crankshaft to the turbine shaft hydrokinetically, thus permitting hydrokinetic torque multiplication to occur when the torque converter operates in a torque multiplication mode.
The clutch is disengaged by increasing the control pressure in the cavity between the clutch plate and the adjacent wall. This causes cooling oil to circulate throughout the friction discs. That fluid is added to the flow of fluid in the torus cavity and circulated through the torous circuit into an oil cooler.
When the control pressure in the pressure cavity behind the piston plate decreases, the clutch is applied by controlling the control pressure. The degree of engagement may be controlled if continuous slipping is desired. The pressure may be modulated in accordance with the driving conditions to effect a continuous slip. This complements the cushioning action and the damping effect of the spring cushion and damper assembly that connects the drive plate to the turbine shaft.
U.S. Pat. No. 4,199,047 shows another lock-up clutch arrangement. That patent also is assigned to the assignee of this invention. Unlike the construction of the '389 patent, the construction of the '047 patent has a clutch piston plate that is stroked toward the turbine rather than toward the converter housing. A friction ring carried by the impeller housing at the outer extremity of the housing is situated directly adjacent the friction surface carried by the piston plate.
A portion of the fluid circulated through the torus circuit flows across the clutch surfaces and radially inward through a control pressure space between the impeller housing and the clutch plate. The flow through the control pressure space is radially inward in contrast to the radial outward flow in the construction of the '389 patent.
It is desired to apply the clutch described in the '047 patent, the control pressure is increased relative to the static pressure and the torus circuit. This also is in contrast to the mode of operation of the construction of the '389 patent where the control pressure in the control pressure cavity is decreased relative to the static pressure in the torus circuit upon application of the clutch.
In both of the constructions of the '047 and '389 patents, a continuous flow of fluid through the control pressure cavity is required during clutch disengagement. If continuous slipping is desired and if the control pressure in the control pressure cavity is controlled accordingly, continuous flow through the pressure cavity likewise is required.